The invention relates to a safety arrangement for a hydrostatic machine connected to a pressure network with impressed pressure.
Secondarily controlled drive systems according to the preamble are known (DE-OS 3,441,185). The speed regulation is by means of a controller to which a plurality of input quantities are supplied as electrical signals, in particular the desired value for the speed and the actual value thereof picked up at a tachogenerator. With the output signal of the controller a proportional valve is driven which controls the fluid paths between a fluid source and a tank and the adjustment means of the hydrostatic machine. A pivot angle is thus set which corresponds to a predetermined absorption volume of the machine. A certain speed of rotation then arises depending on the magnitude of the load to be driven.
In such secondarily controlled drives there is a danger that on failure of a component of the electronic control means or on breakage of a cable the adjustment means for the pivot angle of the machine is so set that the drive motor undergoes maximum acceleration and assumes an inadmissibly high speed of rotation. Thus, speed changes of zero to 10000 rpm can occur within 100 ms.
To avoid this, for safety reasons multiply redundant electronic safety circuits are necessary which however still do not ensure absolute safety.
The invention is therefore based on the problem of providing for a secondarily controlled hydrostatic machine a mechanical-hydraulic safety circuit which reliably detects an inadmissible increase in the speed of rotation and prevents inadmissibly high speeds.